Heretofore, an exhaust gas purifying device provided in an exhaust channel of an internal combustion engine has included a carrier (honeycomb carrier) on which an exhaust gas purifying catalyst is supported, and a tubular case member that houses the carrier. Upon housing the carrier inside the case member, it is important to reliably retain the carrier inside the case member. To retain the carrier inside the case member, a method is sometimes adopted which provides a sloped part where a circumferential face of the case member near each of openings on the exhaust gas-inlet and outlet sides of the case member is narrowed in such a manner as to reduce the diameter toward an open end. In this case, the corresponding carrier side is also provided with a chamfered part, which is a sloped surface corresponding to the sloped part of the case member. The chamfered part on the carrier side is caught on a sloped part-inner face of the case member, whereby the position of the carrier inside the case member is retained.
In order to reliably retain the carrier inside the case member, it has been known to interpose a retaining member commonly called a mat between a case member inner circumferential face and a carrier outer circumferential face. The retaining member needs to have power for retaining the position of the carrier, and resistance to wind erosion occurring from exposure to an exhaust gas flow. If an end of the retaining member is sufficiently recessed from each of positions on the inlet-side end face and outlet-side end face of the carrier, wind erosion is suppressed, as a matter of course. However, recession of the end of the retaining member reduces the carrier position-retaining power of the retaining member, and impairs the original function of the retaining member. Meanwhile, a clogging may be provided in a region having a constant width on the outer circumferential side of the carrier, to sufficiently suppress occurrence of wind erosion of the retaining member. However, the clogging part reduces the effective volume of the carrier.
The present applicant has proposed a technique for solving the above problem (e.g., Japanese Patent Application Publication No. 2016-217305). In the technique of Japanese Patent Application Publication No. 2016-217305, a reduced-diameter part having a smaller inner diameter than the outer diameter of a center part of the aforementioned inlet-side end face of the carrier is formed, near each of the openings on the exhaust gas inlet and outlet sides of the case member. Wind erosion of the retaining member is suppressed by narrowing the exhaust gas stream at the reduced-diameter part. The technique also ensures retention of the carrier inside the case member.